1. Field of Invention
The invention relates to a power supply system including a fuel cell and a battery, and a control method thereof.
2. Description of Related Art
A fuel cell obtains an electromotive force when an electrochemical reaction of a fuel gas including hydrogen and an oxidizing gas including oxygen occurs. In a fuel cell system, hydrogen, which is drawn out from a hydrogen tank, is used as the fuel gas, and compressed air which is taken in by an air compressor is used as the oxidizing gas.
When the fuel cell is activated, operations of drawing out the hydrogen from the hydrogen tank and driving the air compressor are simultaneously started. For a while after the fuel cell is activated, the amount of the supplied fuel gas and the supplied oxidizing gas may not reach the amount necessary to generate electric power (target electric power) required by a load. For example, since it takes a predetermined time until the air compressor reaches a state (steady state) in which the air compressor can take in a predetermined amount of oxygen after being activated, the amount of the oxidizing gas may become insufficient in the fuel cell during the predetermined period of time. When the amount of the supplied fuel gas and oxidizing gas becomes insufficient with respect to the target electric power, trouble such as a voltage drop is caused in the fuel cell. Therefore, there is related art in which electric power (target amount of electric power generation) that needs to be generated by the fuel cell is set based on a flow rate of the fuel gas and the oxidizing gas which are actually supplied so as to prevent the amount of the gas from becoming insufficient.
However, when the target amount of electric power generation is set based on the amount of the actually supplied gas, the target electric power which is required by the load cannot be sufficiently obtained within the predetermined period of time after the activation of the fuel cell. Accordingly, for example, when the fuel cell system is mounted as a power supply for driving a vehicle, sufficient acceleration performance cannot be obtained within the predetermined period of time after the activation of the fuel cell arises.